High vacuum electron tube with magnetically isolated control electrode

ABSTRACT

In a high vacuum electron control tube, a cathode comprised of a plurality of spaced parallel cathode wires or filaments arranged upon a generally cylindrical surface parallel to the cylinder axis cooperates with a common generally cylindrical anode concentric with the cathode structure and a control electrode composed of a plurality of planar loop-shaped control elements each arranged radially between adjacent pairs of cathode wires. Suitable oriented U-shaped metallic screens surrounding each of the cathode wires and a homogeneous magnetic field extending parallel to said wires coact to cause the electrons emitted from each cathode wire to follow cycloidal paths towards said anode with a minimum of electrons reaching said control electrode even in case of relatively high positive control voltages, while at the same time ensuring a high amplification factor of the tube.

United States Patent Inventor Alexander Rusterholz, deceased late of Zurich, Switzerland by Beatrix A. Elsasser-Rusterholz, sole heir Appl. No. 827,126 Filed May 20, 1969 Patented Oct. 5, 1971 Assignee Holding AG. Glarus, Switzerland Priority May 21, 1968 Switzerland 7552/68 HIGH VACUUM ELECTRON TUBE WITH MAGNETICALLY ISOLATED CONTROL Patelhold Patentverwertungs-Elekto- Primary Examiner-Roy Lake Assistant ExaminerPalmer C. Demeo Attorney-Greene & Durr ABSTRACT: In a high vacuum electron control tube, a cathode comprised of a plurality of spaced parallel cathode wires or filaments arranged upon a generally cylindrical surface parallel to the cylinder axis cooperates with a common generally cylindrical anode concentric with the cathode structure and a control electrode composed of a plurality of planar lO0p-shaped control elements each arranged radially between adjacent pairs of cathode wires. Suitable oriented U-shaped metallic screens surrounding each of the cathode wires and a homogeneous magnetic field extending parallel to said wires coact to cause the electrons emitted from each cathode wire to follow cycloidal paths towards said anode with a minimum of electrons reaching said control electrode even in case of relatively high positive control voltages, while at the same time ensuring a high amplification factor of the tube.

PATENTED 0m 5m SHEET 1 BF 2 TAkL M771 ATTORNEY of the same issue) the stream emitted by the cathode. The'effect HIGH VACUUM ELECTRON TUBE WITH MAGNETICALLY ISOLATED CONTROL ELECTRODE The present invention relates to high vacuum electron control tube, more particularly of the type including an anode, a thermionic cathode, a grid or control electrode, and means to provide a magnetic field actingon the electron stream emitted by said cathode and accelerated towards said anode, to deflect said stream away from said control electrode, to reduce the number of electrons from reaching said control electrode, especially wherethe latter is operated at relatively high positive potential. This in turn results in a reduction of the power necessary to control or drive the tube.

As is well known, in connection with specific operations of a high vacuum power tube, appreciable power losses may occur in the grid or control circuit of the tube, such as in the case of the end or, power stage of a transmitting amplifier. In order to produce a desired output power, it has 'been found no longer possible to operate the tube with a negative grid bias, in an effort to minimize the power consumption in the grid circuit, but rather to drive the grid or the like control electrode to relatively high positive potentials during operation, commonly known as Class-C operation of the tube.

In order to reduce the driving power occasioned by the use of a positive control electrode potential, a tube has already been proposed (see for example the articleby .LA. Radmer appearing in the periodical "Cathode Press," Volume 20 of I965, No. 2, page 22, and the article by H. Langer on page 3l thermionic cathode of which consists of a series of cathode wires arranged parallel to the wires of a control grid and each in front of -an interval between two neighboring control grid wires. With the help of a permanent magnet a magnetic field is produced of which the lines of force run parallel to the general direction of the electron discharge of this field is to constrain the electrons emitted by the cathode and accelerated in the direction of the anode, to followhelical paths, the diameters of which, provide an appropriately strong magnetic field intensity, are so small, that, despite a positive grid potential, practically all the electrons pass between the interstices of the grid wiresand practically no current flow occurs in the grid circuit.

A disadvantage of this known tube is that, due to the relatively large separation between adjacent grid wires, the effect of an anode voltage change on the potential at a point in the vicinity of the cathode relative to the effect of an equivalent grid voltage change on the potential at the same point is correspondingly large, which leads to a relatively small amplification factor of the tube. As a further disadvantage, the increase of the electron transit time resulting from the extension of the electron paths occasioned by their helical paths produces a reduction of the power output, especially at the higher operating frequencies.

In order to reduce or obviate the foregoing defects and drawbacks, a vacuum tube construction has already been proposed, as described in my copending Pat. application Ser. No. 712,451, filed Mar. 12, 1969, now U.S. Pat. No. 3,562,576, entitled VACUUM TUBE WITH CONTROL ELECTRODE ISOLATED FROM THE ELECTRON STREAM BY Magnetic DEFLECTION in which all of the electrodes with the exception of the anode draw only negligible electron currents even when operated at relatively high positive biasing potentials.

More particularly, the tube according to the copending application contains, arranged along a first cylindrical surface and turned towards a centrally located .control electrode, a plurality of discrete spaced anode surface portions and a thermionic cathode arranged between each pair of anode surface portions. In addition, there are provided a plurality of screening electrodes each positioned between a thermionic cathode and the adjacent anode surface portions, said screening electrodes extending into the space between the control electrodes and the anode portions to an extent that, in the no-current condition of the tube, the ratio of the electric potential or two anodes within and outside the field strength change produced at a point in the vicinity of the cathodes per unit of control voltage to the field strength produced at the same point per unit anode voltage is approximately equal to the desired amplification factor of the tube. This effect is produced by the magnetic field of which the lines of forceare parallel to the cylindricalelectrode surfaces.

In a tube of the foregoingtype'and forming the subject of the copending application, the electrons emerging frorn the thermionic cathodes describe approximately cycloidal paths under the influence of the magnetic field. As a consequence, even with positive control voltages, the electrons are substantially deflected from the control electrodes, which leads to a corresponding reduction in the driving power for a required high-frequency output power of the tube. On the other hand, the amplification factor attainable with such a tube and deter- -minedby the aforementioned field strength ratio near the cathode surface, is relatively low on'account of the specific geometry of the electrode structure involved.

Accordingly, an important object of the present invention is the provision of a high vacuum'electron control tube of the referred'to type in which, in order to reduce the grid driving power, the electrons are largely withheld from the grid or control electrode by means of a magnetic deflecting field, on the one hand, and which tube at the same time possesses a relatively high amplification factor, on the other hand.

The invention, both as to the foregoing anclancillary objects as well as novel aspects thereof, will be better understood from the following detailed description, taken in conjunction with the accompanying drawings forming part of this disclosure and in which:

FIG. 1 is a longitudinal cross section through one embodiment of a high vacuum electron control tube constructed in accordance with the principles of the invention;

FIG. 2 is a cross-sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is a section similar to FIG. 2 and showing a modification of the tube according to the invention; and

FIG. 4 shows a section also similar to FIG. 2 and illustrating still another modification of a tube construction according to the invention. I

Like reference numerals denote like parts in the different views of the drawings.

With the foregoing objects in view, the invention, according to one of its aspects, involves generally the provision of an electron control tube of the referred to type embodying a preferably cylindrical' fiele'ctrode structure comprising essentially a cathode composed of the plurality of spaced cathode wires arranged up'on a cylindrical surface parallel to the cylinder axis, a common cylindrical anode concentric to said cathode, and a control electrode composed of a plurality of planar control grids or loops each being arranged radially in respect to said axis and between a pair of adjacent cathode wires. The anode advantageously surrounds the cathode and grid structure, but may be disposed within said structure, or grid and cathode may be utilized for the attainment of increased output power of the tube. i

A magnet, preferably in the form of an electromagnetic solenoid concentric to and surrounding the electrode structure, serves to produce a homogeneous magnetic field in the axial direction of the structure of sufficient strength, to cause the electron discharge streams emitted by said cathode wires to follow cycloidal paths towards said anode. This deflection of the electron streams, supplemented by the effect of U- shaped or the like metal screens partly enveloping the cathode wires and being properly oriented with their open portion or apertures in respectto' said anode, results in the electrons of said streams being substantially prevented from reaching the .grids, to thereby reduce the power losses in the grid or control circuit of the tube to'a minimum, on the one hand, while at the same time allowing 'of an effective control of the potential near the cathodes as-a result of the position and planar construction of the grid electrodes, to result in a high amplification factor of-the tube, on the other hand. The aforementioned efi'ect and result may be further enhanced by the provision of a helical or the like concentric screen or suppressor grid interposed between the cathode and grid structure, on the one hand, and the anode, on the other hand, this and other novel features and advantages of the invention becoming more ap parent from the ensuing description in reference to the drawings.

The tube shown in FIGS. 1 and 2 includes a central control electrode structure 1 which is connected by way of a tubular glass insulator 2 with the base 3 of the tube envelope. This control electrode structure consists of a hollow cylindrical body 4 which carries, in the direction of the tube base, an extension in the form of a tube 5 having a closed end. The body 4 is fitted with a plurality of radially outwardly extending plates 6 to the ends of each of which are secured a plurality of spaced and radially extending generally U-shaped wire loops or planar grid elements 7, plates 6 provided with the loops 7 each forming one of the control electrodes 8 of the tube.

Arranged between two adjacent control electrodes 8 is a thermionic cathode in the form of an axially tensioned cathode wire or filament 9. To support the cathode wires 9, arranged upon a cylindrical surface and parallel to the cylinder axis, there is provided a frame or supporting structure consisting of a series of plates 10, ll, 12, 13 and 14 which are connected with one another by a number of spacing rods l5, l6 and 17 of which rods 16 consist of ceramic or an equivalent insulating material.

Frame -14, being suitably suspended from the base 3, carries at its lower end, by means of ceramic insulators 18, a common cathode plate 19 and carries, at its upper end, for axial movement in insulating bushes 20 and 21 secured in the plate II and 10, cathode supporting rods 22.

While, in the example shown, the cathode wires 9 are arranged along a pitch circle, it is understood that the construction may deviate from the circular arrangement. In an extreme case, the cathode wires may be arranged in a linear array and cooperating electrodes and supporting structure modified accordingly.

Each cathode wire 9 which is secured at one end to the common cathode plate 19 and at its other end to the respective cathode supporting rod 22, is held under tension by means of a spring 23 interposed between an upper flange of the rod 22 and an insulating bush 21 mounted in the supporting plate 10. The cathode rods 22 are connected, by way of flexible leads or connections 24 alternately with one and the other of a pair of cathode connecting or terminal rings 25 and 26. The cathode connecting rings 25 and 26 are in turn supported by cathode connecting posts 27 one of which only appears in FIG. 1, since the posts are mutually displaced about the axis of symmetry of the structure by 90. Connecting posts 27 pass through the tube base 3 to which they are sealed by glass insulator tubes or sleeves 28. The spacing rods 17, connecting the mounting plates 12 and I3, carry metal screens 29 of U- shaped cross section the open sides or apertures of which, in the arrangement according to FIG. 2, face in the direction tangential to the pitch circle of the cathode wires 9 and embrace each a respective one of cathode wires 9 to an efiective angle of about 250. The metal screens 29 are connected, by way of the spacing rods 17, plates 12 and a flexible lead or connection 43 with a screening electrode terminal post 44 being led through the tube base 3 from which it is insulated by a tubular glass insulator 45.

The control electrodes 8 and the cathode wires 9 with their U-shaped screens are surrounded by a fourth common and concentric preferably helically shaped screen grid 30 which is provided at its lower end with a cup-shaped grid header 31 and is connected at its upper end with the tube base by way of a conical mounting member 32, whereby to be at ground or zero potential. If desirable, the screen grid 30 may be connected to a separate terminal post for operation at a potential different from ground. For clarity of illustration, the support rods 30' of the screen grid 30 are not shown in FIG. 1. The electrode system 8, 9, 29, 30 supported by the tube base 3 is arranged concentrically within an anode cylinder 34 closed at its lower end 33, while its upper end is connected with the tube base 3 by way of a cylindrical glass insulator 35.

A magnetic field of which the lines of force extend parallel to the axis of the tube or electrode structure is generated by a solenoid coil 43 in which the anode cylinder 34 is concentrically disposed. Cooling of the tube may be effected in a conventional manner by means of a suitable cooling medium, for example water, which flows in an annular gap between the solenoid 43 and the anode 34. In order to improve the cooling effect, the anode may be provided in a known manner with cooling fins (not shown).

The mode of operation of the tube described is as follows:

In the no-current condition of the tube, the ratio of the electric field strength E, at a point in the vicinity of the cathode wires 9 caused per unit of control voltage to the field strength E caused at the same point per unit of anode voltage is approximately equal to the amplification factor of the tube. Since the apertures of the U-shaped screens 29 are in each case turned towards an adjacent control electrode 8, the field strength E. is practically unaffected by the presence of the screens. The through-grip" efi'ect of the anode voltage on the cathode, being determined by the ratio of the effects on the potential near the cathode of equal changes of anode and grid voltages, respectively, that is, in other words the field E on the other hand, is greatly reduced by the screen grid 30, being at least approximately at cathode potential, and by the screens 29, in such a manner that a relatively high amplification factor results. Due to the effect of the axial magnetic field, the electrons emitted by the cathodes 9 move in approximately cycloidal paths toward the anode 34, as shown at A in FIG. 2. The strength of the magnetic field is adjusted, by regulation of the current through the solenoid 43, to a value such that, even with the highest positive control potential encountered in operation, practically no electrons reach the control electrodes 8, due to the curvature of the electron paths, whereby no noticeable current flow will occur in the grid or control circuit of the tube. By controlling the potential on the screens 29 to be at a negative or small positive value relative to ground or cathode, resulting in a displacement of the operating characteristic curves of the tube, it can be arranged that for zero control voltage the anode current also becomes zero.

In order to reduce the intensity of the magnetic field necessary to produce electron paths of cycloidal form, according to a modified construction of the tube as shown by FIG. 3, the plane of symmetry of the aperture of the screens 29' is, in contrast to the arrangement described in references to FIGS. I and 2, inclined or angularly displaced in the outward direction to the tangent of the pitch circle of the cathode wires 9, the displacing angle being advantageously between 10 and 40. In this modified tube, a reduction of the amplification factor, as compared with the embodiment according to FIGS. 1 and 2, must be expected.

The U-shaped screens 29 and 29' according to the described embodiments of the tube of the invention have the effect that the control voltage draws substantially more electrons from the side of the cathode wires which are turned towards the aperture of the screens that from the side which is turned away from said aperture. The electron emission from the side turned away from the aperture is therefore utilized to a substantially lesser degree than that from the side turned towards the apertures of the screens.

In the alternative embodiment of the tube according to the invention as shown by FIG. 4, improved utilization of the electron emission is achieved. In this modified tube construction the electrode system is mounted within an annular space enclosed by two concentric cylindrical anode parts 37 and 38. Between each pair of electrode wires 9', arranged along a concentric pitch circle in the same manner as in the preceding embodiments, there is provided a planar control electrode or grid 36 extending essentially in the radial and axial directions and being supported by separate mounting rods 36'. On either side of this series of cathode wires 9' and control electrodes 36 are situated the inner and outer ring-shaped parts 37 and 38,

respectively, forming a composite anode body. Between each anode part 37 and 38, on the other hand, and the cathode wires 9' and control electrodes 36, on the other hand, there is provided respectively helically shaped screen grids 39, 40. Each cathode wire 9 is positioned between two parallel screening plates 41 and 42 supported by rods 41' and 42' and disposed at angles of about l040 with the tangent to the pitch circle of the cathode wires. In this case, the electrons emitted from the cathode wires 9' are accelerated towards both neighboring control electrodes 36, following approximately cycloidal paths towards the anodes, as indicated at B in FIG. 4.

Since in a high vacuum thermionic tube of the type described, the screen grid arranged between the anode and the remaining electrodes is at least approximately at cathode or ground potential, a substantial decoupling of the electric fields of the anode and the control is possible without resorting to the known grounded-grid mode of operation.

In the foregoing the invention has been described in reference to an exemplary illustrative device. It will be evident, however, that variations and modifications, as well as the substitution of equivalent parts for those shown for illustration, may be made without departing from the broader scope and spirit of the invention.

I claim:

1. A high vacuum electron control tube comprising:

1. a cathode structure including a plurality of spaced cathode wires arranged upon the surface of a spacial cylinder with each of said wires disposed parallel to the axis of said cylinder,

2. a common cylindrical anode disposed concentrically with said cathode structure,

3. a control electrode structure including a plurality of planar control elements extending radially in respect to said axis and each between a pair of adjacent cathodes wires,

4. means to provide a homogeneous magnetic field in a direction generally parallel to said cathode wires and permeating the space enclosed by said wires and said anode, and

5. a plurality of metal screens arranged each to partially shield one of said cathode wires, to cause, in cooperation with said field, the electrons of the discharge current emitted by said wires to follow cycloidal paths towards said anode, substantially without reaching said control element.

2. A high vacuum electron control tube as claimed in claim 1, wherein said control electrode structure further contains a cylindrical supporting member disposed along said axis and each of said control elements comprises a plurality of spaced oblong wire loops radially extending from said member, and

wherein said anode encloses both-said control electrode structure and said cathode structure.

3. A high vacuum electron control tube as claimed in claim 1, wherein each of said control elements consists of at least one supporting rod parallel to said axis and a plurality of spaced oblong wire loops affixed to and radially extending from said rod.

4. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with their apertures oriented towards said anode.

5. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a substantially U-shaped cross section with an effective opening aperture extending over approximately 250 and are arranged with said apertures oriented towards said anode.

6. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with the axes of their apertures pointing in the direction of the tangent to the pitch circle of said cathode wir s.

7? A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with the axes of their apertures pointing towards said anode and forming an angle of from 10 to 40 with the tangent to the pitch circle of said cathode wires.

8. A high vacuum electron control tube as claimed in claim 1, wherein said anode consists of a pair of cylindrical anode members disposed respectively inside and outside of said cathode and control electrode structures, and wherein each of said screens consists of two planar elements disposed on either side of the respective cathode wires, to cause a pair of cycloidal-shaped electron discharge streams emanating from the opposite sides of said wires to both said anode members.

9. In a high vacuum electron control tube comprising;

i. a cathode structure including a plurality of spaced and parallel cathode wires,

2. an anode having a substantially smooth surface cooperating with and substantially equally spaced from said cathode wires,

3. a control electrode structure including a plurality of planar control elements each extending centrally of and transversely to the connecting line transverse to a pair of cathode wires,

4. means to provide a homogeneous magnetic field extending in the direction of said wires and permeating the space enclosed by said cathode structure and said anode, and

5. a plurality of metal screens arranged each to partially shield one of said cathode wires, to cause, in cooperation with said field, the electrons of the discharge current emitted by said wires to follow cycloidal paths towards said anode, substantially without reaching said control elements. 

1. A high vacuum electron control tube comprising:
 1. a cathode structure including a plurality of spaced cathode wires arranged upon the surface of a spacial cylinder with each of said wires disposed parallel to the axis of said cylinder,
 2. a common cylindrical anode disposed concentrically with said cathode structure,
 3. a control electrode structure including a plurality of planar control elements extending radially in respect to said axis and each between a pair of adjacent cathodes wires,
 4. means to provide a homogeneous magnetic field in a direction generally parallel to said cathode wires and permeating the space enclosed by said wires and said anode, and
 5. a plurality of metal screens arranged each to partially shield one of said cathode wires, to cause, in cooperation with said field, the electrons of the discharge current emitted by said wires to follow cycloidal paths towards said anode, substantially without reaching said control element.
 2. a common cylindrical anode disposed concentrically with said cathode structure,
 2. an anode having a substantially smooth surface cooperating with and substantially equally spaced from said cathode wires,
 2. A high vacuum electron control tube as claimed in claim 1, wherein said control electrode structure further contains a cylindrical supporting member disposed along said axis and each of said control elements comprises a plurality of spaced oblong wire loops radially extending from said member, and wherein said anode encloses both said control electrode structure and said cathode structure.
 3. A high vacuum electron control tube as claimed in claim 1, wherein each of said control elements consists of at least one supporting rod parallel to said axis and a plurality of spaced oblong wire loops affixed to and radially extending from said rod.
 3. a control electrode structure including a plurality of planar control elements each extending centrally of and transversely to the connecting line transverse to a pair of cathode wires,
 3. a control electrode structure including a plurality of planar control elements extending radially in respect to said axis and each between a pair of adjacent cathodes wires,
 4. means to provide a homogeneous magnetic field in a direction generally parallel to said cathode wires and permeating the space enclosed by said wires and said anode, and
 4. means to provide a homogeneous magnetic field extending in The direction of said wires and permeating the space enclosed by said cathode structure and said anode, and
 4. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with their apertures oriented towards said anode.
 5. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a substantially U-shaped cross section with an effective opening aperture extending over approximately 250* and are arranged with said apertures oriented towards said anode.
 5. a plurality of metal screens arranged each to partially shield one of said cathode wires, to cause, in cooperation with said field, the electrons of the discharge current emitted by said wires to follow cycloidal paths towards said anode, substantially without reaching said control elements.
 5. a plurality of metal screens arranged each to partially shield one of said cathode wires, to cause, in cooperation with said field, the electrons of the discharge current emitted by said wires to follow cycloidal paths towards said anode, substantially without reaching said control element.
 6. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with the axes of their apertures pointing in the direction of the tangent to the pitch circle of said cathode wires.
 7. A high vacuum electron control tube as claimed in claim 1, wherein said screens have a U-shaped cross section and are arranged with the axes of their apertures pointing towards said anode and forming an angle of from 10* to 40* with the tangent to the pitch circle of said cathode wires.
 8. A high vacuum electron control tube as claimed in claim 1, wherein said anode consists of a pair of cylindrical anode members disposed respectively inside and outside of said cathode and control electrode structures, and wherein each of said screens consists of two planar elements disposed on either side of the respective cathode wires, to cause a pair of cycloidal-shaped electron discharge streams emanating from the opposite sides of said wires to both said anode members.
 9. In a high vacuum electron control tube comprising; 